Adverse event reporting in patients treated with levothyroxine: results of the pharmacovigilance task force survey of the american thyroid association, american association of clinical endocrinologists, and the endocrine society.

Objective: To survey physicians to determine whether potency and consistency issues with levothyroxine sodium (LT4) have been resolved and to assess current experience regarding safety of substituting LT4 products.

Methods: Members of the American Association of Clinical Endocrinologists, American Thyroid Association, and The Endocrine Society collaborated to create a survey instrument that would effectively sample the clinical experience of their society members and frequent prescribers of LT4. More than 18,000 e-mailed requests for information were generated, and the Web sites of each society provided links to the data collection form. The survey provided an opportunity to collect clinical observations of adverse events or product availability problems from physicians caring for patients with thyroid disease who required use of contemporary LT4 preparations.

Results: After adjustment for known reasons for unstable results from thyroid function tests, 199 reports of adverse events associated with changes in thyrotropin values were further analyzed. One hundred seventy-seven reports (88.9%) were associated with a change in the source of LT4; no change was noted in 21 (10.6%). Details regarding the circumstances of the change were provided in 167 of the 177 reports (94.4%), The reporting physicians themselves or their office staff had changed the LT4 preparation in only 1 of the 167 cases (0.6%). The remainder of changes had been made by the patient's pharmacy, either with the physician's knowledge (in 13 of 167 cases [7.8%]) or without his/her knowledge (in 153 of 167 cases [91.6%]). Fifty-four of 199 cases (27.1%) described serious adverse events; 52 of these (96.3%) were associated with a substitution of one LT4 preparation for another.

Conclusions: The clinical use of contemporary LT4 products continues to be associated with some adverse outcomes. A small number of reports were associated with continued use of the same LT4 products. The most frequently reported adverse outcomes were associated with the approved generic substitution of LT4 products, frequently without the prescribing physician's knowledge.